"Low bus voltage" warning light

[Pass-A-Frozo]

Warning light + Don't know what it means + Don't know what effect it will have on my flight = Don't takeoff

If they made it a warning or caution light they probably thought you should know what effect that problem will have on flying.

I definately think you did the right thing.

What's that saying.. "Better to be on the ground wishing you were flying, than flying and wishing you were on the ground"

Not to mention: "I had this problem" .. CFI: Ahh silly bugger you could have gone flying

is much better than

"I had this problem" .. CFI: "You went flying with that?!?!?!"

I doubt you'll find someone complaining "I have a student and he's far too cautious!"

[Chimbu chuckles]

ME at your level of experience you did FAR and away the best thing you could have done.

I would like to add some thoughts though just as points of discussion...hopefully the same stuff your instructor might suggest come Monday.

You really should know what every light means and the things that might trigger activation. Move heaven and earth if necesary to acheve this knowledge...buy a good LAME coffee/beer,or oral sex if that is what it takes , to pick his brains.

I have no idea what aeroplane you're talking about but I would suggest that the Low Bus Voltage warning light is designed to catch your attention and then send you to the Volt/Ammeter. It's activation might be caused by,

Stuck Relay,
Alternator/generator stuffed, or not earthed,
Battery stuffed, or not earthed,
Bus bar fault. Perhaps a wiring fault/short...may trip CB but maybe not.

If the Volt/ammeter meter reads zero or a discharge I would cycle the BATT/ALT switches off, wait 10 seconds, the ON. That could resolve the situation completely by resetting the relay and allowing it to work the second time around but you would only know if you knew the correct minimum and maximum voltage it should be indicating (at appropriate RPM) and the light extinguished. You might trouble shoot further with the Volt/ammeter by turning stuff like landing lights, pitot heat etc on and noting the effect if you're somewhat unconvinced as to whether you have resolved the problem or not...switch them on and note a flicker of the ammeter needle and then an increase showing the system is taking the load and increasing output to cope.

If the Volt/Ammeter continues to read very low volts or discharge on the ammeter you are stuffed and taxiing back in....but when you get back in you will be armed with info to give to the engineer..."Well the Low Bus Voltage light came on. It was Indicating X Volts at Y RPM and increasing RPM caused the light to blink off and on. I cycled the electrical switches and checked CBs but no joy".

Instead of.

"The Low Bus Voltage light came on...what does that mean?"

The first approach wins friends among the engineers..particularly if you hang around and show interest in the answers that come from the trouble shooting...the second convinces them that every negative thought they ever had about pilots was correct

If you think there was no mag drop between left and right try selecting off momentarily...if the engine runs on normally you have a dangerous problem and need to taxi back, shut down and get an engineer. If the engine dies select back to both then recheck left and right alternately but slowly...leave it selected at each mag for a good long time and really carefully note RPM. How much rpm drop you get is not that important, despite what you may have been told, but you must get some. It may have just been you were getting a very small drop and not noticing it because you were selecting back and forth a little quickly.

Hope this helps...well done though.

[Pass-A-Frozo]

Originally Posted by Chimbu chuckles

You really should know what every light means and the things that might trigger activation. Move heaven and earth if necesary to acheve this knowledge...buy a good LAME coffee/beer,or oral sex if that is what it takes , to pick his brains.

You're really a lonely LAME aren't you Chimbu

[Woomera]

Its disappointing you did not receive full instruction on all cockpit instruments and warning devices before going cross country.

There is no doubt you did the right thing turning back.

Rely on the engineers, but in an alternator (as distinct from a DC generator) equipped aircraft a flickering low voltage light appears to indicate either a faulty connection or faulty voltage regulator. An alternator will generally charge (i.e. produce higher than battery voltage) at engine idle, whereas a DC generator will not produce a charge at engine idle speed.

You didn't say whether the light went out when higher RPM was applied - that could give better indication of the cause of the problem.

Murphy's Law would ensure the voltage regulator or faulty connection would have failed totally immediately after take off!

Sunny Woomera

[M.25]

Originally Posted by multi_engined

one other thing I forgot to note when I was completing my run ups that I didn't get a drop in rpm when I was checking the L and R magnetos.

The whole point of doing runups is to alert the pilot of any irregularities BEFORE he/she leaves the ground. What is the point of doing them if you are just going to take off anyway?

Re the warning light: If you were taxiing for takeoff and observed a warning light that you didn't understand, regardless of what it was, why would you takeoff? Especially in a situation where there is absolutely no pressure to continue. The least that you could do is taxi back in, find a comfy chair, make a coffee and pull out the POH to educate yourself on what the light actually means.

You made a good decision in turning back.

Did your instructor give you a debrief???